diff --git a/lib/client.js b/lib/client.js
index ffe6dfe..41eb476 100644
--- a/lib/client.js
+++ b/lib/client.js
@@ -436,11 +436,12 @@ export default class Client extends EventTarget {
 
 	setCaseMapping(name) {
 		this.cm = irc.CaseMapping.byName(name);
-		this.whoisDB = new irc.CaseMapMap(this.whoisDB, this.cm);
 		if (!this.cm) {
 			console.error("Unsupported case-mapping '" + name + "', falling back to RFC 1459");
 			this.cm = irc.CaseMapping.RFC1459;
 		}
+
+		this.whoisDB = new irc.CaseMapMap(this.whoisDB, this.cm);
 	}
 
 	isMyNick(nick) {